@[toc]
Pre
org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor
注意下： Initialization 表示 初始化 （意思是对象已经生成） 。 Instantiation 表示 实例化 （意思是对象还未生成） 。
接口继承了BeanPostProcess接口 , 从方法上我们也可以看出 InstantiationAwareBeanPostProcessor 做了一些扩展 。
BeanPostProcess接口只在bean的初始化阶段进行扩展（注入spring上下文前后），而InstantiationAwareBeanPostProcessor接口在此基础上增加了3个方法，使得扩展接口可以在实例化阶段和属性注入阶段
该类主要的扩展点有以下5个方法，主要在bean生命周期的两大阶段：实例化阶段 和初始化阶段 ，
(1)实例化: 实例化的过程是一个创建Bean的过程,即调用Bean构造函数,单例的Bean入单例池中
(2)初始化: 初始化的过程是一个赋值的过程,即调用Bean的setter方法,设置Bean属性
InstantiationAwareBeanPostProcessor作用于过程(1)实例化前后; BeanPostProcessor用于过程(2)初始化前后
按调用顺序，我们来看一下
postProcessBeforeInstantiation：实例化bean之前，相当于new这个bean之前postProcessAfterInstantiation：实例化bean之后，相当于new这个bean之后postProcessPropertyValues：bean已经实例化完成，在属性注入时阶段触发，@Autowired,@Resource等注解原理基于此方法实现postProcessBeforeInitialization：初始化bean之前，相当于把bean注入spring上下文之前postProcessAfterInitialization：初始化bean之后，相当于把bean注入spring上下文之后
InstantiationAwareBeanPostProcessor 注册过程源码分析
我们还是从
org.springframework.context.support.AbstractApplicationContext#refresh开始看 ，主要是下面两个方法
.......
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
.......
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
看下调用栈
org.springframework.context.support.PostProcessorRegistrationDelegate#registerBeanPostProcessors()
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
org.springframework.beans.factory.support.AbstractBeanFactory#getBean
org.springframework.beans.factory.support.AbstractBeanFactory#doGetBean
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#createBeancreateBean跟进去
@Override
protected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException {
// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
if (bean != null) {
return bean;
}
//省略....
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
return beanInstance;
}
通过上面的代码，我们可以看到在执行doCreateBean之前有resolveBeforelnstantiation方法; 看注释
// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.resolveBeforelnstantiation判断执行InstantiationAwareBeanPostProcessor.postProcessBeforelInstantiationg接口方法实现;doCreateBean创建bean方法;
postProcessBeforeInstantiation的执行时机源码解析
org.springframework.context.support.PostProcessorRegistrationDelegate#registerBeanPostProcessors()
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
org.springframework.beans.factory.support.AbstractBeanFactory#getBean
org.springframework.beans.factory.support.AbstractBeanFactory#doGetBean
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#createBean
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#resolveBeforeInstantiation重点看 resolveBeforeInstantiation
/**
* Apply before-instantiation post-processors, resolving whether there is a
* before-instantiation shortcut for the specified bean.
* @param beanName the name of the bean
* @param mbd the bean definition for the bean
* @return the shortcut-determined bean instance, or {@code null} if none
*/
@Nullable
protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
Object bean = null;
//如果beforeInstantiationResolved还没有设置或者是false（说明还没有需要在实例化前执行的操作）
if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
// Make sure bean class is actually resolved at this point.
// 判断是否有注册过InstantiationAwareBeanPostProcessor类型的bean
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
Class<?> targetType = determineTargetType(beanName, mbd);
if (targetType != null) {
//执行
bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
if (bean != null) {
bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
}
}
}
mbd.beforeInstantiationResolved = (bean != null);
}
return bean;
}继续 applyBeanPostProcessorsBeforeInstantiation
/**
* Apply InstantiationAwareBeanPostProcessors to the specified bean definition
* (by class and name), invoking their {@code postProcessBeforeInstantiation} methods.
* <p>Any returned object will be used as the bean instead of actually instantiating
* the target bean. A {@code null} return value from the post-processor will
* result in the target bean being instantiated.
* @param beanClass the class of the bean to be instantiated
* @param beanName the name of the bean
* @return the bean object to use instead of a default instance of the target bean, or {@code null}
* @see InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation
*/
@Nullable
protected Object applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass, String beanName) {
// 循环处理
for (InstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().instantiationAware) {
Object result = bp.postProcessBeforeInstantiation(beanClass, beanName);
//只要有一个result不为null；后面的所有 后置处理器的方法就不执行了，直接返回(所以执行顺序很重要)
if (result != null) {
return result;
}
}
return null;
}当然了也有 postProcessAfterInitialization
@Override
public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
for (BeanPostProcessor processor : getBeanPostProcessors()) {
Object current = processor.postProcessAfterInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}使用场景 ： 创建代理类
package com.artisan.bootspringextend.testextends;
import com.artisan.bootspringextend.service.ArtisanServiceImpl;
import com.artisan.bootspringextend.service.ClassA;
import com.artisan.bootspringextend.service.ClassAInterceptor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.BeansException;
import org.springframework.beans.PropertyValues;
import org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor;
import org.springframework.cglib.proxy.Enhancer;
import org.springframework.context.annotation.Configuration;
/**
* @author 小工匠
* @version 1.0
* @description:
* @date 2022/11/28 0:33
* @mark: show me the code , change the world
*/
@Slf4j
@Configuration
public class ExtendInstantiationAwareBeanPostProcessor implements InstantiationAwareBeanPostProcessor {
private static final String VALUE = "classA";
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
if (VALUE.equals(beanName)) {
log.info("4 beanName {}-----> postProcessBeforeInitialization", beanName);
}
return bean;
}
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (VALUE.equals(beanName)) {
log.info("5 beanName {}-----> postProcessAfterInitialization", beanName);
}
return bean;
}
@Override
public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
if (beanClass == ClassA.class) {
log.info("1 beanName {} -----> postProcessBeforeInstantiation", beanName);
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(beanClass);
enhancer.setCallback(new ClassAInterceptor());
ClassA classA = (ClassA) enhancer.create();
log.info("proxy created ---->{}", classA.toString());
return classA;
}
return null;
}
@Override
public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
if (VALUE.equals(beanName)) {
log.info("2 beanName {}-----> postProcessAfterInstantiation", beanName);
}
return false;
}
@Override
public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) throws BeansException {
if (VALUE.equals(beanName)) {
log.info("3 beanName {} -----> postProcessProperties", beanName);
}
return pvs;
}
}
我们可以看到 InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation 生成了代理类后，直接执行了 初始化后的动作 BeanPostProcessor#postProcessAfterInitialization 。
